Production tubing can be positioned in a downhole environment of a wellbore in a fluid-producing formation. Fluid from the formation can travel through the production tubing to a surface of the wellbore. The production tubing can include a safety valve that is controllable by hydraulics, electrical signals, or another control mechanism. The safety valve may be a sub-surface safety valve. The safety valve can open to allow fluid to flow through the production tubing. The safety valve can close to prevent fluid from flowing through the production tubing.
For example, in response to an accident, a control action at the surface, or otherwise a decrease of hydraulic fluid pressure, the safety valve can allow a flow tube that is part of the safety valve and the production tubing to move toward the surface, resulting in a flapper to close and seal the flow tube (and thus the production tubing) from fluid from the formation.
A closing flapper or other closing mechanism can exert force on the flow tube, which may result in damage to the flapper assembly, a pressure spike in a control line for the hydraulic fluid, and other undesirable results. For example, as the flapper is close to closing, the pressure differential across the flapper can force the flow tube toward the surface with a large amount of force. The large amount of force may break the flapper or seat hinge, shear a hinge pin, warp the flow tube, and impart momentum into the flow tube. In some situations, 1250 pound force (lbf) is transferred to the flow tube for every 100 psi of pressure differential across the flapper.
Safety valves are desirable that can handle forces from flappers or other closing mechanisms during closing.